Basic concepts and laws of chemical thermodynamics

Сентябрь 8, 2022

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Basic concepts and laws of chemical thermodynamics

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2. Chemical thermodynamics is a science of transformations of energy: heat into other forms of energy, amount
3. SYSTEM AND ITS SURROUNDINGS: A system in thermodynamics refers to that part of universe in which
4. boundary SYSTEM surroundings (environment) boundary (surface) SUBSTANCE ENERGY
5. PHASE is a set of homogeneous parts of a heterogeneous system, with identical physical and chemical
6. Water in contact with its vapour in a closed insulated vessel is an isolated system Hot
7. By the nature of the interaction with the surroundings thermodynamic systems are divided into 3 types:
8. The set of all physical and chemical properties of the system describes its thermodynamic state. State
9. Chemical potential Concentration Density (or specific gravity) Ductility Elasticity Hardness Melting point and boiling point Pressure
10. Any change of parameter in the system called the thermodynamic process. Major Types of Thermodynamic Processes:
11. THERMODYNAMIC PROCESS ISOTHERMAL (T=const) ISOBARIC (Р=const) ISOCHORIC (V=const) ADIABATIC PROCESS (Q = 0) No heat exchange
12. Define Reversible and Irreversible Process There are two main types of thermodynamic processes: reversible process and
13. The main processes in chemical thermodynamics are: isobaric-isothermal (P, T = const) isochoric-isothermal (V, T =
14. Main objective of thermodynamics is to be able to determine if a reaction will occur when
15. THERMODYNAMIC FUNCTIONS PROCESS FUNCTIONS: Q – HEAT, A – WORK STATE FUNCTIONS: U – Internal energy,
16. Function of the state is the total energy of the system: E = K + P
17. In thermodynamics, the internal energy (U) of a thermodynamic system is the total kinetic energy due
18. The U is essentially defined by the 1st law of thermodynamics which states that energy is
19. Thus heat Q is given the system and consumed to increase the internal energy ΔU and
20. The molar heat of formation of a compound (ΔHf) is equal to its enthalpy change (ΔH)
21. Experiment on determining heat (Q) of reaction for MgSO4 (s) + 7H2O → MgSO4.7H2O
22. A calorimeter is a device used to measure the quantity of heat flow in a chemical
23. HESS’S LAW overall heat change of a chemical reaction is independent of its pathway, energy change
25. Q = – Δ Н If the reaction is generated heat (Q>0), enthalpy of the system
26. Enthalpy of reaction using combustion data
27. THE 2nd LAW OF THERMODYNAMICS All spontaneous processes are irreversible (e.g. heat flows from hot to
28. Entropy Entropy is a thermodynamic property that measures the degree of randomization or disorder at the
29. The standard entropy of reaction (ΔS0) is the entropy change for a reaction carried out at
30. The Second Law of Thermodynamics The entropy of the universe increases in a spontaneous process and
31. The 3rd Law of Thermodynamics and Absolute Entropy The entropy of a perfect crystalline substance is
32. G – Gibbs Free Energy Predicts the direction of a spontaneous reaction. Uses properties of the
33. Standard Free-Energy Changes The standard free-energy of reaction (ΔG°reac) is the free-energy change for a reaction
34. Factors Affecting ΔG
35. Thermodynamic Equilibrium A system is said to be at thermodynamic equilibrium when all of its macroscopic
36. 0eth Law of Thermodynamics: Two systems in thermal equilibrium with a third system are in thermal
37. Free Energy and Chemical Equilibrium ΔG = ΔG0 + RT lnq R is the gas constant
38. Free Energy and Chemical Equilibrium
39. QUIZ ME NEXT cooking involves chemical changes helped by a rise in temperature 1 A pressure
40. QUIZ ME NEXT 2 Which one is not a state function? Heat (q) Volume Internal energy
41. QUIZ ME NEXT Isothermal process 3 When no heat energy is allowed to enter or leave
42. QUIZ ME 4 A well stoppered thermos flask contains some ice cubes. This is an example
43. GLOSSARY OF LECTURE 1. Thermodynamics: Energy differences and transfers between systems. 2. Systems: Isolated system: “have
44. 5. Work (w): “The transfer of energy from one mechanical system to another. It is always
46. Скачать презентацию

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Chemical thermodynamics is a science of transformations of energy: heat into

other forms of energy, amount of heat gained or released from a system, a spontaneity of a reaction, Gibbs free energy function, relationship between Gibbs Free Energy and chemical equilibrium.
The object of the study is - thermodynamic system – the physical body (matter) or a group of bodies (the set of substances) that are in interaction, mentally or really isolated from the environment (surroundings)

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SYSTEM AND ITS SURROUNDINGS:
A system in thermodynamics refers to that part

of universe in which observations or study are made and remaining universe constitutes the surroundings.
The surroundings include everything other than the system.
System and the surroundings together constitute the universe:

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boundary
SYSTEM
surroundings
(environment)
boundary (surface)
SUBSTANCE
ENERGY

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PHASE is a set of homogeneous parts of a heterogeneous system,

with identical physical and chemical properties, and separated from other parts through visible surfaces

PHYSICAL STATES OF THE SYSTEM

HETEROGENEOUS SYSTEM

HOMOGENEOUS
SYSTEM

Is a system without surfaces separating the different properties of the system (phase)

Is a system, within which there is a surface separating the different properties of the system

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Water in contact with its vapour in a closed insulated vessel

is an isolated system

Hot water in contact with its vapour in a closed container

water in an open beaker is an open system as it can exchange both energy and matter with the surrounding

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By the nature of the interaction with the surroundings thermodynamic systems

are divided into 3 types:
Open: Mass and Energy can transfer between the System and the Surroundings
Closed: Energy can transfer between the System and the Surroundings, but not Mass
Isolated: Neither Mass nor Energy can transfer between the System and the Surroundings

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The set of all physical and chemical properties of the system

describes its thermodynamic state. State of the system is described by thermodynamic parameters and functions.
All quantities characterizing any macroscopic property of the system is called state parameters.

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Chemical potential
Concentration
Density (or specific gravity)
Ductility
Elasticity
Hardness
Melting point and boiling point
Pressure
Specific

energy
Specific heat capacity
Specific volume
Spectral absorption maxima (in solution)
Temperature
Viscosity

Energy
Entropy
Gibbs energy
Length
Mass
particle number
number of moles
Volume
electrical charge
Weight

INTENSIVE PROPERTIES

EXTENSIVE PROPERTY

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Any change of parameter in the system called the thermodynamic process.
Major

Types of Thermodynamic Processes:
Adiabatic process - a process with no heat transfer into or out of the system.
Isochoric process - a process with no change in volume, in which case the system does no work.
Isobaric process - a process with no change in pressure.
Isothermal process - a process with no change in temperature.

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THERMODYNAMIC PROCESS
ISOTHERMAL
(T=const)
ISOBARIC
(Р=const)
ISOCHORIC
(V=const)
ADIABATIC PROCESS
(Q = 0)
No heat exchange between
the system and

the surroundings

Processes in which the system
returns to its original state
after a series of successive
transformations, called
cyclic process
or thermodynamic cycle

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Define Reversible and Irreversible Process
There are two main types of thermodynamic

processes: reversible process and the irreversible process.
Processes in which both the system and its surroundings can be simultaneously returned to their initial states after the process has been completed are called a reversible process.
Processes in which the system and its surroundings cannot be simultaneously returned to their initial states after the process has been completed are called a irreversible.

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The main processes in chemical thermodynamics are:
isobaric-isothermal (P, T = const)
isochoric-isothermal

(V, T = const)
All chemical reactions take place under these conditions.

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Main objective of thermodynamics is to be able to determine if

a reaction will occur when reactants are brought together under certain conditions.
Non-spontaneous Reaction – a reaction does not occur under specific conditions.
Spontaneous Reaction – a reaction does occur under specific conditions:
A waterfall runs downhill
A lump of sugar dissolves in a cup of coffee
At 1 atm, water freezes below 0ºC and ice melts above 0ºC
Heat flows from a hotter object to a colder object
Iron exposed to oxygen and water forms rust

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THERMODYNAMIC FUNCTIONS
PROCESS FUNCTIONS:
Q – HEAT,
A – WORK
STATE FUNCTIONS:
U –

Internal energy,
H – Enthalpy,
S – Entropy,
G – Gibbs free energy,

Derivative quantities, dependent on the parameters of the system state and immeasurable by direct methods are called thermodynamic functions:

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Function of the state is the total energy of the system:

E = K + P + U
In thermodynamics, state function is a property of a system that depends only on the current state of the system, not on the way in which the system acquired that state. A state function describes the equilibrium state of a system.
In contrast, process quantities – mechanical work and heat are not properties of the system, they characterize the process of energy exchange between the system and the surroundings, therefore they depend on the path (specific transition) of the process.

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In thermodynamics, the internal energy (U) of a thermodynamic system is the total kinetic energy due to the

motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of atoms within molecules and crystals. It includes the energy in all the chemical bonds, and the energy of the free, conduction electrons in metals.
U is a state function of a system, and is a extensive quantity. The SI unit [U]=Joule.

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The U is essentially defined by the 1st law of thermodynamics which states that energy is conserved «The increase

in internal energy of a closed system is equal to the difference of the heat supplied to the system and the work done by it»:
ΔU = Q – A
where:
ΔU is the change in internal energy of a system during a process;
Q is heat "added to" a system (measured in joules in SI);
A is the mechanical work "done on" a system (measured in joules in SI)

THE 1st LAW OF THERMODYNAMICS

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Thus heat Q is given the system and consumed to increase

the internal energy ΔU and to perform work against external forces A:
Q = ΔU + A
For isobar-isothermal process: p, Т = const
ΔU = U2final — U1initial
Аgas = р ⋅ΔV => ΔV = V2final – V1 initial
Q = ΔU + A => Q = (U2 — U1) + (рV2 — рV1)
Q = (U2 + рV2 ) — (U1 + рV1) => Q = -Δ Н
U + pV = H – Enthalpy function

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The molar heat of formation of a compound (ΔHf) is equal

to its enthalpy change (ΔH) when one mole of compound is formed at 25°C and 1 atm from elements in their stable form.

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Experiment on determining heat (Q) of reaction for
MgSO4 (s) +

7H2O → MgSO4.7H2O

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A calorimeter is a device used to measure the quantity of

heat flow in a chemical reaction. Two of the most common types of calorimeters are the coffee cup calorimeter and the bomb calorimeter.

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HESS’S LAW
overall heat change of a chemical reaction is independent

of its pathway,
energy change in changing A + B → C + D is the same regardless of the route (independent of route) by which the chemical changes occurs.

Hess’s Law – used to calculate ΔH for reaction which cannot be determined experimentally

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Q = – Δ Н
If the reaction is generated heat (Q>0),

enthalpy of the system is lowered (ΔH<0), in this case the reaction is called exothermic.
If the reaction is absorbed heat (Q<0), the system increases the enthalpy (ΔH>0), and it called the endothermic reaction.

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Enthalpy of reaction using combustion data

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THE 2nd LAW OF THERMODYNAMICS
All spontaneous processes are irreversible (e.g. heat

flows from hot to cold spontaneously and irreversibly)
To predict spontaneity we need:
Change in enthalpy.
Entropy – a measure of the randomness or disorder of a system: ↑ disorder = ↑ entropy

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Entropy
Entropy is a thermodynamic property that measures the degree of randomization or

disorder at the microscopic level. The natural state of affairs is for entropy to be produced by all processes.
A macroscopic feature which is associated with entropy production is a loss of ability to do useful work. Energy is degraded to a less useful form, and it is sometimes said that there is a decrease in the availability of energy.
Entropy is an extensive thermodynamic property. In other words, the entropy of a complex system is the sum of the entropies of its parts.
The notion that entropy can be produced, but never destroyed, is the second law of thermodynamics.

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The standard entropy of reaction (ΔS0) is the entropy change for

a reaction carried out at 1 atm and 250C:

Standard Entropy

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The Second Law of Thermodynamics
The entropy of the universe increases in

a spontaneous process and remains unchanged in an equilibrium process. (Clausius)
"It is impossible in any way to diminish the entropy of a system of bodies without there by leaving behind changes in other bodies" (Planck)
"In any irreversible process the total entropy of all bodies concerned is increased." (Lewis)

Spontaneous process:

ΔSuniv = ΔSsys + ΔSsurr > 0

Equilibrium process:

ΔSuniv = ΔSsys + ΔSsurr = 0

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The 3rd Law of Thermodynamics and Absolute Entropy
The entropy of a

perfect crystalline substance is zero at the absolute zero of temperature
Absolute zero is −273.15 °C (degrees Celsius), or −459.67 °F (degrees Fahrenheit) or 0 K (kelvin).

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G – Gibbs Free Energy
Predicts the direction of a spontaneous reaction.
Uses

properties of the system to calculate.
For a constant pressure-temperature process:

ΔGT = ΔHsys – TΔSsys

ΔG < 0 The reaction is spontaneous in the forward direction.
ΔG > 0 The reaction is nonspontaneous as written. The reaction is spontaneous in the reverse direction.
ΔG = 0 The reaction is at equilibrium.

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Standard Free-Energy Changes
The standard free-energy of reaction (ΔG°reac) is the

free-energy change for a reaction when it occurs under standard-state conditions.
Standard free energy of formation (ΔG°) is the free-energy change that occurs when 1 mole of the compound is formed from its elements in their standard states.

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Factors Affecting ΔG

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Thermodynamic Equilibrium
A system is said to be at thermodynamic equilibrium

when all of its macroscopic properties are time-independent and remain so when the system is isolated from its surroundings.
Thermodynamic equilibrium, in simple words is, same temperature. At same temperature bodies do exchange heat but do not gain or lose heat.
The system is said to be in thermodynamic equilibrium if the conditions for following three equilibrium is satisfied:
1) Mechanical equilibrium
2) Chemical equilibrium
3) Thermal equilibrium

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0eth Law of Thermodynamics:
Two systems in thermal equilibrium with a

third system are in thermal equilibrium to each other.

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Free Energy and Chemical Equilibrium
ΔG = ΔG0 + RT lnq
R

is the gas constant (8.314 J/K•mol)
T is the absolute temperature (K)
q is the reaction quotient
K is the equilibrium constant of reaction

At Equilibrium: ΔG = 0 => q = K
0 = ΔG0 + RT lnK
ΔG0 = – RT lnK

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Free Energy and Chemical Equilibrium

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QUIZ ME
NEXT
cooking involves chemical changes helped by a rise in temperature
1 A

pressure cooker reduces cooking time for food because …

heat is more evenly distributed in the cooking space

boiling point of water involved in cooking is increased

the higher pressure inside the cooker crushed the food materia

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QUIZ ME
NEXT
2 Which one is not a state function?
Heat (q)
Volume
Internal energy (E)
Enthalpy

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QUIZ ME
NEXT
Isothermal process
3 When no heat energy is allowed to enter or

leave the system, it is called:

Irreversible process

Adiabatic process

Reversible process

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QUIZ ME
4 A well stoppered thermos flask contains some ice cubes. This

is an example of a …

Non-thermodynamics system

Closed system

Open system

Isolated system

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GLOSSARY OF LECTURE
1. Thermodynamics: Energy differences and transfers between systems.
2. Systems:
Isolated

system: “have walls or boundaries that are rigid, do not permit transfer of mechanical energy, perfectly insulating, and impermeable. The have a constant energy and mass content.
Adiabatic systems: Perfectly insulated systems.
Closed systems: have walls that allow transfer of energy in or out of the system but are impervious to matter. They contain a fixed mass and composition, but variable energy.
Open Systems: have walls that allow transfer of both energy and matter to and from the system.
3. Equilibrium: “A system at equilibrium has none of its properties changing with time”. A system at equilibrium will return to that state after being disturbed.
4. State Variables: Variables that define the state of a system.
Extensive variables are proportional to the quantity of matter being considered (V, total Cp).
Intensive variables are independent of quantity (concentration, viscosity, density, molar Cp)

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5. Work (w): “The transfer of energy from one mechanical system

to another. It is always completely convertible to the lifting of a weight”. “The energy that flows across a system boundary in response to a force moving through a distance (such as happens when a system changes volume”.
6. Heat (q):
“The transfer of energy that results from temperature differences”.
“The energy that flow across a system boundary in response to a temperature gradient.”
“That part of any energy transfer that is not accounted for by mechanical work (FxD).”
q=∆U-w
7. Heat Capacity: The relation between heat transferred to a body and the change in T.
8. Enthalpy: The increase in enthalpy of a system is equal to the heat absorbed at constant pressure, assuming the system does only PV work.
9. Entropy: A measure of the loss of capacity of the system to do work.
10. Gibbs free energy is a measure of the potential for reversible or maximum work that may be done by a system at constant temperature and pressure. It is a thermodynamic property that was defined in 1876 by Josiah Willard Gibbs to predict whether a process will occur spontaneously at constant temperature and pressure.

Basic concepts and laws of chemical thermodynamics

Содержание

Chemical thermodynamics is a science of transformations of energy: heat into

SYSTEM AND ITS SURROUNDINGS: A system in thermodynamics refers to that part

boundarySYSTEMsurroundings(environment) boundary (surface)SUBSTANCE ENERGY

PHASE is a set of homogeneous parts of a heterogeneous system,

Water in contact with its vapour in a closed insulated vessel

By the nature of the interaction with the surroundings thermodynamic systems

The set of all physical and chemical properties of the system

Chemical potential ConcentrationDensity (or specific gravity) DuctilityElasticityHardnessMelting point and boiling pointPressureSpecific

Any change of parameter in the system called the thermodynamic process. Major

THERMODYNAMIC PROCESSISOTHERMAL(T=const)ISOBARIC(Р=const)ISOCHORIC(V=const)ADIABATIC PROCESS(Q = 0)No heat exchange between the system and

Define Reversible and Irreversible Process There are two main types of thermodynamic

The main processes in chemical thermodynamics are:isobaric-isothermal (P, T = const)isochoric-isothermal

Main objective of thermodynamics is to be able to determine if

THERMODYNAMIC FUNCTIONSPROCESS FUNCTIONS: Q – HEAT, A – WORKSTATE FUNCTIONS:U –

Function of the state is the total energy of the system:

In thermodynamics, the internal energy (U) of a thermodynamic system is the total kinetic energy due to the

The U is essentially defined by the 1st law of thermodynamics which states that energy is conserved «The increase

Thus heat Q is given the system and consumed to increase

The molar heat of formation of a compound (ΔHf) is equal

Experiment on determining heat (Q) of reaction for MgSO4 (s) +

A calorimeter is a device used to measure the quantity of

HESS’S LAW overall heat change of a chemical reaction is independent

Q = – Δ НIf the reaction is generated heat (Q>0),

Enthalpy of reaction using combustion data

THE 2nd LAW OF THERMODYNAMICS All spontaneous processes are irreversible (e.g. heat

EntropyEntropy is a thermodynamic property that measures the degree of randomization or

The standard entropy of reaction (ΔS0) is the entropy change for

The Second Law of ThermodynamicsThe entropy of the universe increases in

The 3rd Law of Thermodynamics and Absolute EntropyThe entropy of a

G – Gibbs Free EnergyPredicts the direction of a spontaneous reaction.Uses

Standard Free-Energy ChangesThe standard free-energy of reaction (ΔG°reac) is the